1. Field of the Invention
The present invention relates to a fuel pump for drawing a fuel such as gasoline etc., increasing the pressure thereof, and discharging this pressurized fuel.
2. Description of the Related Art
A known fuel pump generally comprises a substantially disc-shaped impeller and a casing. The impeller is rotatably disposed within the casing. Groups of concavities are formed along the circumference direction of the impeller. The concavities are repeated in the circumferential direction. A first groove is formed in the front surface of the casing in an area directly facing the group of concavities in the upper face of the impeller. The first groove extends continuously in a circumference direction from an upstream end to a downstream end. A second groove is formed in the back surface of the casing in an area directly facing the group of concavities in the lower face of the impeller. The first groove extends continuously in a circumference direction from an upstream end to a downstream end. A suction hole is formed to pass through the casing for communicating the upstream end of the first groove. A discharge hole is formed to pass through the casing for communicating the downstream end of the second groove.
When the impeller rotates, a fuel is sucked into the casing from the suction hole. The sucked fuel flows along the groove and the concavities of the impeller. Swirl flow occurs between the concavities on the front surface of the impeller and the first groove and swirl flow occurs between the concavities on the back surface of the impeller and the second groove because of the effects of centrifugal force caused by the rotation of the impeller. The pressure of the fuel rises as it flows along the grooves. The fuel that has flowed along the grooves and has been pressurized is discharged out of the casing through the discharge hole.
In this type of fuel pump, swirl flow is created between the groove of the casing and the concavities of the impeller. If the flow of this swirl flow could be improved to reduce energy loss, the efficiency of the fuel pump could be increased. In the fuel pump disclosed in Japanese Laid-Open Patent Publication No. 9-511812, partitioning walls which separate the adjacent concavities of the impeller are at an angle with regard to the rotating shaft of the impeller in order to improve the fuel flow.